1. Field of the Invention
The present invention relates to a push-button switch in which a movable contact is rotated by a constant angular step in one direction by a depression of a push button, and contacted with stationary contacts in accordance with the rotation angle of the movable contact, thereby performing contact switching.
2. Description of the Prior Art
A positioning mechanism is incorporated into a push-button switch of this type. The positioning mechanism includes: a star wheel which is rotated by a constant angular step in one direction through a ratchet mechanism or the like which is operated by a depression of a push button that automatically returns; and an indenter which is configured by a metal ball or the like, and which is pressed against the outer periphery of the star wheel by a spring. A movable contact is attached so as to corotate with the star wheel (see Patent Reference 1).
The star wheel is hardly stopped at a position where a ridge portion is opposed to the indenter, and rotated to a position where a valley portion is opposed to the indenter to cause the indenter to fit in the valley portion, whereby the star wheel is stopped to hold the position of the movable contact in a return state of the push button (see Patent Reference 1).
In a push-button switch of this type, the indenter is caused to be contacted with the outer periphery of the star wheel which has alternately ridge and valley portions, thereby producing a sense of operation. In this case, it is important to prevent a switch operating force required for pushing the push button, from being increased.
Therefore, a star wheel in which ridge and valley portions having a relatively small inclination angle are alternately formed on the outer periphery is used (see Patent Reference 1).
In such a star wheel, however, slopes of the ridge portions have a small inclination angle. When a load of the indenter is applied to the apex of one of the ridge portions, therefore, a balance is easily established, thereby producing a problem in that the star wheel is easily stopped at a position where the ridge portion is opposed to the indenter.
As a conventional technique for solving the problem, a configuration has been proposed where an inflection point is disposed in a middle of a slope of a ridge portion, and the inclination angle of a slope portion extending from the inflection point to the apex of the ridge portion is set so as to be larger than that of another slope portion extending from the inflection point to the valley portion, whereby the indenter is prevented from being stopped at the ridge portion (see Patent Reference 2).
[Patent Reference 1] Japanese Utility Model Application Laying-Open No. 60-15722
[Patent Reference 2] Japanese Utility Model Application Laying-Open No. 5-97028